Vehicles operating in an autonomous mode (e.g., driverless) can relieve occupants, especially the driver, from some driving-related responsibilities. When operating in an autonomous mode, the vehicle can navigate to various locations using onboard sensors, allowing the vehicle to travel with minimal human interaction or in some cases without any passengers.
Motion planning and control are critical operations in autonomous driving. Typically, an autonomous driving vehicle (ADV) is controlled and driven according to a reference line. When generating a driving trajectory, the system heavily relies on the reference line. The reference line is a smooth line on the map. The vehicle tries to drive by following the reference line. Roads and lanes on the map are often represented by a list of connected line segments, which are not smooth and difficult for the ADV to follow. As a result, a smooth optimization is performed on the reference line to smooth the reference line. However, such optimization is time consuming. For example, it may take 0.1 second to smooth a reference line with 100 meters (m) long. A planning cycle for planning a next trajectory is also around 0.1 second, which is not enough to complete the optimization.